Field of the Invention
The present invention relates to image processing of performing region segmentation of an image.
Description of the Related Art
A region segmentation method is used as a technique of dividing an image into regions similar in attribute such as color, texture, or brightness. By performing coding processing, image processing, and image recognition processing for each region divided from the image, the processing amount can be reduced in comparison with a case in which these processes are performed for each pixel. Recently, in a growing number of cases, image processing is performed on a high-resolution image in a built-in device. The region segmentation technique for reducing the processing amount is receiving attention.
A region segmentation method described in literature 1 is a method of performing region segmentation of an image quickly. Literature 1 discloses a region segmentation method by clustering based on the K-Means method using color information and coordinate information. The technique described in literature 1 speeds up processing by restricting the reference range of the representative point of a region serving as a cluster center in a coordinate space.
Literature 1: Radhakrishna Achanta, et al., “SLIC Superpixels Compared to State-of-the-Art Superpixel Methods”, IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 34, No. 11, pp. 2274-2282, November 2012
In region segmentation by clustering described in literature 1 or the like, clustering and update processing of a representative point need to be repeated for each image. When an image present in a main memory is repetitively transferred to a region segmentation apparatus, the transfer band of the main memory increases. If a working memory capable of high-speed processing for buffering an image in the main memory is prepared, and an image is repetitively transferred from the working memory to the region segmentation apparatus, the transfer band of the main memory can be reduced. However, when such a working memory is used, the working memory needs to have a large memory capacity in order to hold all the regions of an image, raising the cost.
In order to reduce the memory capacity of the working memory for buffering an image, it is also effective to divide an image into a plurality of blocks (to be referred to as “block images” hereinafter), and perform region segmentation for each block image. However, when region segmentation is applied to each of the block images, a region boundary arising from the shape of a block appears.
Japanese Patent Laid-Open No. 8-30787 (literature 2) proposes a method of performing region segmentation using a small-capacity working memory. Literature 2 discloses a method of reducing the working memory by repeating clustering and updating of a representative point for each block image. In literature 2, an overlap of pixels is provided between blocks. As for the overlap region, each of a plurality of blocks including this region is subjected to region segmentation processing. The appearance of a region boundary arising from the shape of a block is reduced by referring to even data of a block image having undergone region segmentation, in addition to data of a block image during region segmentation.
However, the region segmentation method by clustering for each block image, which is described in literature 2, requires an overlap of pixels between adjacent block images. When performing region segmentation of a given block image, even an image at a portion overlapping an adjacent block image is referred to, in addition to the given block image. For this purpose, a working memory larger in memory capacity than the block image is necessary.